Method of operating a regenerative furnace for chemical conversions



Oct. 21, 1958 J. w. BEGLEY 2,857,4432

. METHOD oF OPERATING A REGENERATIVE EURNACE FOR CHEMICAL coNvEEsIoNs Filed July v22, 1955 2 sheets-sheet 1 -A T TOR/ver Oct. 21, 1958 J. w. BEC-:LEY 2,857,443

METHOD OF OPERATING A REGENERATIVE FURNACE FOR CHEMICAL CONVERSIONS Filed July 22, 1955 2 Sheets-Sheet 2 M MJAMYM Arron/vir;

ilnited States Patent Ollce i DIETHOD F OPERATING A REGENERATIVE FURNACE FR CHEMICAL CONVERSIONS John W. Bagley, Ann Arbor, Mich., assigner to Phillips Petroleum Company, a corporation of Delaware Application July 22, 1955, Serial No. 523,704- 8 ciaims. (ci. 26o-679)k mixture zone in said furnace Without being preheated, Y* thus increasing the throughput possible and the thermal eiciency in an'operation effected in a reversing regenerative furnace having at least two heat accumulator zones and at least one combustion mixture zone, in which operation alternately air is preheated in a zone, and admixed with a fuel in a combustion zone, and the resulting hot combustion gases are used to preheat a further zone, and then the said zones thus prepared are used to heat, convert, and to quencha material such as a hydrocarbon gas or vapor. ln one embodiment of the invention, said `part of the gas not preheated is introduced directly into the combustion mixture zone with the fuel gas.

In regenerative furnaces, a stream of air and fuel gas is burned in, or hot combustion products are passed through, a refractory checkerwork, thereby heating it to a high temperature. After the hot gases have passed through a checkerwork for a time su'icient to heat it to a kdesired temperature, the flow of combustion gases is terminated, and thereafter a fluid material to be thermally treated is passed through the heated checkerwork to bring the material tothe desired conversion temperature and to maintain it at a desired temperature range for a length of time suicient to accomplish the desired conversion.

-In a particularly useful furnace `of the type'here discussed which is utilized for the endothermie conversion of hydrocarbons, notably for the cracking-of one or more hydrocarbons, such asmethane, ethane, propane, or

Y Patented Oct. 21, 1958 checkerwork to prepare it to receive the hydrocarbon to be preheated and partially cracked orotherwise conl verted therein.

When this checkerwork has attained a sufficiently high temperature, the ilow of air and fuel is stopped, andthe Y material to be cracked or otherwise converted passes in the opposite direction through the just heated checkerwork, the combustion mixture chamber, and finally through the now cooler checkerwork previously employed to preheat the combustionV supporting gas. Y Thus, the hydrocarbon to be converted is first preheated `to a couversion temperature range, converted substantially at said temperature range, and finally the conversion product mixture thus obtained is quenched or cooled to a desired temperature, during its ow through the apparatus.

After a timed conversion period, the flow of materials to be converted is stopped, and combustion-supporting gas is again passed into the apparatus` but in aV direction opposite to that of its first introduction, that is the gas is now passed into the checkerwork which has justi been employed to heat the hydrocarbon -to be converted.` At the same time, fuel gasis introduced into thecombustion chamber to mix with the air and to form a combustible mixture which is burned in said chamber producing hot gases which are passed into a checkerwork section downl stream of the combustion chamber thus heating said last-mentioned checkerwork. When the last-mentioned checkerwork has reached a suilciently. high temperature,

the feed to be converted is passed through, the heated checkerwork, the `combustion zone and finally through the 'other checkerwork, as before, to preheat, convertor crack the same and to quench `the resulting product mixture. l Y Y.

In the consideration of the operation of an apparatus such as just described, I have encountered certain problems. Thus, there is a limit to which the temperature can be raised and/or lowered Without unduly thermally stressing the refractory or other apparatus. construction material which may ,be employed. Thus, it .has 4been found that there is a limit to the amount of heat which may be imparted to the combustion chamberand principally to thecheckerwork to Whichtheicombustion gases are passed from the Vcombustion chamber, Also, upon passing air for combustion purposes through a checkerwork which has 'just been employed to quench converted hydrocarbons, it has been found that there isexperienced too much cooling in the sense that not only Visnthelleat of quench of the converted hydrocarbon removed ,from the checkerwork but. also the refractory of the checker- Work is cooled to a temperature substantiallybelow that to whichit can be cooled Without unduly stressing it Y thermally. There is also'a'tlimit to the rate ottemperbutane, or heavier hydrocarbons, principally in the gaseous phase, to produce unsaturated hydrocarbonssuch as acetylene or ethylene, a zone containing a refractory material, for example an elongated checler'work, is pro'- vided at each end of an intermediate combustion mixture zone, for example a combustion chamber. Combustion supporting gas is passedV in one direction through one yof the checkerworks (which after one cycle of heating contains a substantial amount of heat at an elevated tempe'rature) while a fuel is introduced into the combustion chamber. Fuel gas and air mixture-thus produced Vis burned and products of combustion thus produced are passed through a downstream checkerwork to heat said ature change to which the refractor'ies can be subjected Without undue thermal stress, Thus, for any ,size apparatus the throughput ofhydrocarbon to be'converted is limited by the factors just discussed. Anotherlimiting factor islthe pressure drop encountered when, with a certain apparatus, oW of required quantities, of hot combustion gases'for raising to a conversiontemperature quantities of hydrocarbon considerably in excess ofthe capacity of said apparat-us, when preheating all the air, is attempted. Furthermore, another problem results when .the quantity of air put through preheat in a checkerwork is increased to provide the necessary `combustion gases at a temperature requiredfor convertinganfincreased quantity of hydrocarbon, as'described, employ- 3 ing a desired combustion `or tiring temperature. Thus, it has been found that the thermal eiciency is considerably decreased when the air input to the checkerwork is increased. This, it has been found, is d-ue to the fact that the amount of heat extracted by the air is greater than that put into the refractory of the checkerwork when the hydrocarbon conversion products are quenched therein.V Thus, during heating of the checkerwork with combustiony gases lost heat must be replaced by burningV a'increased quantity of fuel. Since the temperature of the combustion or Vfiring is desirablyV maintained sebstann tially constant at an optimum level for the apparatus, it Afollows that the combustion-supporting gas rate must be increased during the combustion cycle. These and other problems, then, are required to be solved for such an apparatus having fixed physical characteristics, and for an operation effected therein, inwhich operation there are valternatelypracticed two cycles, one cycle in which in a r'st zone a combustion-supporting' medium is preheated, then passed into a combustion mixture zone from which hot combustion gases, produced by burning of a fuel, are passed into another zone to preheat the same for an ensuing conversion at an elevated temperature and another cycle in which a material is passed into said Vanother'zone to preheat it and at least partially convert it, then through said combustion zone to complete the desire'd conversion ofV said material and then converted (material is passed into said iirst'zone to quench said maferial to a desired lower temperature, and in which each ensuing alternate conversion cycle is effected by ow of material to be converted through the apparatus in the opposite direction to the last.

According to the present invention, there is provided an improved method for the conversion of a uid Vin a regenerative furnace of the general character just described, i.e., a furnace in which a combustion mixture chamber or Zone is located intermediate refractory check- Verw'orks or heat accumulator zones, in each of which alternately a conversion is endothermically effected yby passing said fluid through a first refractory checkerwork or zone, Va combustion mixture chamber or zone, and thereafter throughV another refractory checkerwork or lzone, in a cyclic operation, such as previously described,

wherein, as stated, endothermic conversion cycles are alternated with exothermic heating cyclesras heretofore described, which comprises preheating in said first zone Vonly a portion, preferably a minimum portion, of the combustion air required, the minimum portion being thatrequired to remove the hydrocarbon lquench heat' and passing lanother portion of the required combustion airfto said combustion zone withoutrpassing it through said first zone. Ordinarily, Ia predetermined ratio of preheated air to air not preheated is employed, although it is also possible to vary this ratio during a combustion cycle Aas will be understood, i Y

Operation according ltoV the present invention permits a substantially increased quantity of fluid ormaterial or hydrocarbon to be converted in an apparatus of given Vsize without encountering the problems setoutrherein and Vproblems `related to them. Apparatus of a smaller size can be designed in the light of this invention to handleu the same charge rate as previously couldv be` handled by prior art apparatus and methods; or existing apparatus can be modified to handle a greater throughput,

. Further, in'view ofthe decreased thermal stresses yrealized when lEiperating according to the concepts of the invention, cheaper refractories' can be employed in the furnace construction. f

i AThe advantages of my process which are obtained byV preheatingonly a portion of the combustion-supporting gas, contrary to prior art methods, andV introducing the othen rtion of the combustion-supportingvgas into the combustion mixture` zone into :which the fuel gas is valso iiitoduced, lare further Aapparent from that which follows. Atwthe outset among the important advantages of my selectively connectedV uf'ithreflluentcenduit 2e by three process are. included greater furnace capacity, greate thermal efficiency, decreased pressure drop, and a sub,-v stantial reduction in thermal fractories, which last result 1s of great practical imf portance.

shock or strainon the re-4 Other advantages as well as aspects and objects of the invention are apparent from a study of the disclosure, i g

the drawings, and the appended claims.

My processr is Iapplicable not only to an endothermic -1 hydrocarbon conversion cyclically alternated with a period work for preheating while-a second reactant fluid and, fluid'are introduced, into an intermediate zione, in a manner analogous to the Y Y introduction of a-combustion-supporting lluidand a fuel v another portion of the rst reactant gas as described hereinbefore. The two reactant iuids react exothermically 1n the intermediate zone, which, in- Y stead of being termed aV combustion mixture zone o r chamber, is termed a reaction zone or chamber. i an e'xiithermicy chemical reaction between the fluids occurs in the reaction mixture zone thus furnishing het to that zone and the downstream checkerwork.

In the interest of simplicity and clarification, in'vention will be hereafter described in one important aspectt:

involving thermal conversion of hydrocarbons" in the gase, ous phase. Y

The invention is particularly applicable to therthe'rmal cracking of streams containing methane,vethane, propane,

Thus, 1

a second huid. In such a butane, or isobutane, .or to streams comprising mixtures of two or more of these componds, to produceun-` saturated hydrocarbons, andY in particular to produce- Y acetylene or ethylene, or mixturesv offb'oth. i A Y In Figures l, 2 and 3 are shown one form of apparatus in which the process of the invention can Abe practiced.A4

Figure 1 is an elevation, partially in section, of asuit;

able regenerative furnace for use in accordancewiththis invention. Figure 2 is an isometric'view of two tiles placed together. Figure 3 is a partial cross-section of Figure .1,

taken at 33. Figure 4 graphically illustrates somead-fj,

vantages of the inveniton. y i

Referring' to the drawing,ra regenerative furnace :2 8

comprises a steel shell 1, insulatingA refractory Vv2, andV heat accumulating refractory checkerworks' 3 and g4 sepia-V, Y rated by a combustion mixture chamber y5. The heat exe.v l Y changing refractory checkerworks are made up `of tiles.V

Figure 2 shows two of the tiles stacked `so that the sernifV i 'i Y' circular grooves in the upper yand lower surfaces of Vthe i tiles form circular tubes across the-depth'of theftile'.'`

The grooves onthe tile are staggered so Ythatthe tube i centers formed by the stacksof the tiles are about equally spaced. 'Figure 3 shows the arrangement of the tubes formedV b`y the tile checkerwork, andfuel and airimani- :i Y folds. `Communicating with Vcombustion mixture'rcharnf.

ber 5 through'ports ,17 are fluid introduction rheans' and manifold conduit Y22 via auxiliary lines32,.jConduiy 19 and 2,2"contain flow control V'n 1ea`n s, j9 and 10, respectively, which means can bemotor valves;r and commun cate with conduits 18 and 2,1, respectively.

.which in turn' communicate with manifoldY conduit`19.V`V Y bers l5 and 2d, respectively'.Y Ccnduits fi and Y2.5 are also way valve 6. Timerll isoperativelyr connected tollow.

in hot refractory 8, thereby providing means for sequentially changing the cycles of operation of the regenerative furnace. Qperation of the process my invention will be described as it is carried out in the form of apparatus shown in Figure l, and as Vapplied to the regenerative cracking of hydrocarbons:

I. COMBUSTION CYCLE (FLOW LEFT TO RIGHT) Valves 6, 7 and 8 are turned `opposite to position shown in Figure 1. Valves 9 and 10 are open, these changes being effected by timer 11. Air to be preheated ows through line 12, valve 8, line 1 3, valve 7 and line 14 to plenum chamber 15, thence through hot refractory tubes 16 in refractory mass 4 to combustion mixture chamber 5. The preheated air supplements fuel and air entering ports 17 by way of line 18, valve 9, manifold 19 and lines 20, in the case of fuel, and by Way of line 21, valve manifold 22 and auxiliary lines 32 Vconnecting manifold 22 with lines 20, in the case of air. The hot combustion gases pass through tubes 23 in refractory mass 3 and heat the said mass 3 to reaction temperature. The cool combustion gases leave by way of plenum chamber 24, line 25, valve 6 and line 26 to utilization as fuel or disposal as desired.

II. MAKE CYCLE (FLOW RIGHT TO LEFT) At the beginning of this cycle, the timer operates to close valves 9 and 10 and to reverse plug valves 6, 7 and 8 (position shown in Figure l). Hydrocarbon feed, t0- gether with steam if desired, enters line 27 and passes by way of Valve 8, line 13, valve 7 and line 25 to plenum chamber 24. The hydrocarbon feed passes through hot refractory mass 3 by way of tubes 23 wherein it is heated to reaction temperature and cracked. The cracking continues until the reactants have passed through combustion mixture zone 5 and into tubes 16 of refractory mass 4. The refractory mass V4, which Was considerably cooled by preheating the air used in the combustion cycle now quenches the products of the cracking reaction which continue on out of refractory mass 4 by way of plenum chamber 15, line 14, valve 6, and line 26 to product recovery means (not shown).

III. COMBUSTION CYCLE (FLOW RIGHT TO LEFT) At the beginning of this cycle, the timer operates to reverse plug valve 8 and to open the valves 9 and 10. Air enters line 12 and passes by Way of valve 8, line 13, valve 7, line 25 and plenum chambery 24 to hot refractory mass 3 which it traverses by way of tubes 23. The air is e preheated in the refractories 3 and cools the refractory IV. MAKE CYCLE (FLOW LEFT TO RIGHT) The timer operates to reverse valves 6, 7 and 8 and to close valves 9 and 10. Hydrocarbon feed, and steam if desired, enters by way of line 27, valve 8, line 13, valve 7, line 14, and plenum chamber 15. The feed is crackedV mass 4 by flowing through tubes 16, thence through combustion mixture chamber 5 to tubes 23 in refractory mass 3 whereinV the Y products are quenched. The quenched products pass by way of plenum chamber 24, line 25, valve 6 and line 26 to product recovery. The timer operates to reverse the plug valves 6, 7 and 8 and open valves 9 and 10 and the series of cycles is repeated.

In certain furnaces of this type, useful for the production of acetylene, the conversion Zone is 9" Wide and 20 high, total furnace length being 9 41/2, with a combustion chamber length 9". In a larger scale furnace, suitable dimensions, are a cross-section of 25" by 80" for the conversion zone. 'Ihe proper dimensions, of course, vary with the exact throughput of the furnace, the type of reactants used, thel necessary temperature and. pressure, and various other operating features, as will be understood.

Example Results of calculations showing the advantages of the invention when cracking ethane to produce acetylene in a furnace of the type shown in Figures 1 and 3 are presente in Table 1 and Figure 4. The cross-section of the furnace considered in this study is 27" wide by 90"; The surface area of the tubes formed by the checkerwork was 506 square feet per foot of length. The crosssectional area of the tubes was 3.95 square feet which is 23.4 percent of the total cross-sectional area. The length of each refractory checkerwork tube section was 10.5 ft., and the length of the combustion zone was '2 feet. It will be noted that a constant feet rate of ethane was employed in each example. At a constant firing temperature and exit combustion gas temperature, the lair preheatrtemperature and the exit hydrocarbon temperature will vary as the amount of air to be preheated is varied. Thus, for oneY case the amount of air preheated was varied and the total amount of air required at each air rate was determined. These results were extrapolated to the point where the entire amount of air was preheated; The results are presented in Table l. The results in Table 1 are for a case when the exit combustion gas temperature was 800 F.

Some of the results in Table l are plotted in Figure 4. As shown in Figure 4 the efficiency decreases as the amount of air preheated is increased. The maximum efficiency is obtained when the minimum amount of air is preheated. The minimum .amount of air is defined as that amount required to remove the Ihydrocarbon quench heat. The thermal etiiciencydecreased from 54 percent to 30 percent when the amount of air preheated was increased from the minimum to the amount required when the entire amount of air was preheated. This may seem to be anomalous but it can be explained. As the amount of air preheated is increased above the minimum amount, the amount of heat transferred from the refractory of either section to the air (depending on which end the air enters the furnace) is increased but the heat of quench is not increased significantly. Dur-V heat losses were due to the increased amount of combustion gases leaving the furnace at the constant temperature of -800 in the cases considered here. Y

Other results presented n Figure 4 are the total air required and the maximum temperature change inthe refractory when the amount of air preheated is varied. For this case when the entire amountof airV was preheated, 1,200,000 pounds ofrair per day were required. The pressure ,drop ,acrossV the furnace wouldv prohibit operation at the lforegoing ethane feed rate when the entire amount of air is preheated.y However, the capacity would be greater than the 72,450 pounds per day if the minimum amount of air were preheated and additional air introduced at the midde of the furnace with the fuel. Y It is to be noted that if the, amount of air preheated is between the minimum and the -amount vrequired when all of the air is preheated, theratio of the air tofuel introduced at the center of the furnace is belowV` the theoretical air-fuel ratio in most cases (see YTable 1).- Because'V of the high temperatures presented at these airhereaftenlis not nou,l preferred.

L EFFECT OF THE AMONT OF AIR PREHEATED Eth'anelFeed Rate, ibi/day 72, 500 72, 450 72, 450 72, 450

Conversion, Percent 92.4 92.4 Length of Each Refractory Section, Feed 1 1,0,.,5f` 10.5 10.5 10.5 Firing Temperature, F 2, 800 2, 800 2, 800 1, 2, 800 E xt Combustion. Gas Teml peratnre, soo 80o soo r soo ExitHydrocarbonTemperalb. day'. l 450,000 G00, 000 i 1, 200, 000 Amount ot Air With Fuel,

1b./day 221, 000 17 2,' 000 132, 500 0 Fuer nate, 1b;/f1ay 9, 24o 12,100 12,440 l 16, 87o Weight of Combustion Gases,

1b.] day 274, 840 634, 100 744, 940 l, 216, 87 0 HeatLosses, MM B t. n./day 99. 505 155. 345 173. 435 253. 663 y Air Preheat Temperature, i

2, 060V 2, 048 2, 040 l, 900 Thermal Efficiency, Percent- 54. 0 40. 3 35. 2 l; 30. 1 Maximum Rate of Refractory t Temperature Change, FL/

Mln 190 248 266 1 326 1 This amount of air: musi; bev preheated in order to maintain the same temperature level in the furnace.

From these examples, it will be seen that, as the amountofair to be preheatedis increased, thermal efciency decreases, thethermal stresses on the refractory increase, and the pressure drop increases; further, the fuel andair. required increase. These factors plus the decreasainetciency as the amount of air4 preheated is increased vilrldicater.advantages.for preheating only the mini-V mum amount of air. The worst case from all standpoints mentioned, it will be seen, is where all of the *air is preheated.` The increase in thermal stresses on the refractory when preheating all the air increases the chance of spallingorbreaking up of the refractory.

It will .be obviousoto those skilled in the art in possessionof the concepts of this invention that calculation need not be .resortedto in order to determine the Yquantity of fuel to be .employed in the combustion cycle when employinga given. ratio of preheated air to air not preheated,J a givenicharge rate of material to be endothermically converted, and a given iiringtemperature, and where a given maximumV temperature of the quenched endothermically converted product material is chosen. Thus,it can be seen, thatthe firing temperaturewill depend upon the ratio of the total amount of air to the amount of fuel. As'. will `befreadily understood, no calculation is necessary since data can be taken from the plant andthe airV to fuel ratio can be adjusted to obtain a particular iiringtemperature. The total amount of fuel, then, to be employed depends, of course, upon the optimumA amount of heat to be applied to the material i' to be endothermically converted. This, of course, can

also be determined by trial and error operation. Thus, at

one particularfuel rate, after the unit is `lined out, data can be taken on the eluent endothermically converted gases produced in the make cycle. rates can be employed using the same rate of material to be converted on the make cycle and analyses of the product gases be again determined. From these data, then, the optimum desired fuel rate can be chosen.

In the no w preferred embodiment Vwhen effecting an endothermic reaction of a hydrocarbon, according tothe inventiona minimum amount of air is preheated, i. e., the Vamount of air which must be preheated by passing through thev refractory section in order to remove enough heat from the refractory so that the refractory will be effective to quench the product endothermically convetred gases to a desired temperature. This minimum amount of air can also be determined, as will be under,- stood, by plant operation. Assuming that one is operatingV above this minimum amount of air, the ratio of air not preheated to air preheated can be increased, still keeping the same fuel rate and ratio of total ,air to fuel. As

will be understood by those in possession of the teachings Y and concepts of'the invention, one will'now have tol decrease the ratio total air to fuel iin order to obtainthel f' Then diiferent fuel same firing! temperature; once this is done, it will'beseen that the amountof-fuel must Anow also be. reducedw atl o the same firing ltemperature because oftheincreased ther-` malfeiiciency as previously discussedV in -connectionwith the resultsshown in Figure 4.V before, the; total arno-unt of fuel necessary at the'new ratio'swill bede-l ter-mined by plant data. ThisA processV of increasing` the, ratio of air not preheated to preheatedrair and lining` the unit out at the new'conditio'nsis repeated until one arrives at thef'rpoint'where the mlnimurn'amountl ofl air isi being used, e., where theV exit endothfermically'converted gases are being quenched just to the desired tern-` perature onpthe lined out operation. Thus, any further, reduction in theamount of air preheated lwill result in the exit converted gases not being'quenched toas low a temperature as desired. o

As will be understood, the preferred numerical'ratiO.

of combustion-supporting gas not preheated to com'buse' tion-supporting gas preheated Vdepends upon many facV Y tors including the particular conversion, the particular physical dimensions of the furnace, etc. However, in the, endothermic conversion of hydrocarbons to produce acetylene or to produce amixture containing acetylene and ally in theY range from Also, in suchvoperatiornthe ratio of Atotal-` combustion-supporting gas to fuel depends upon a largenumber of factors, but usually the ratio of total com-p bustion-supportingrgas used compared to the amount of.l

ethylene, a preferred ratio is usu 3:1 to 7*:1.

combustion-supporting gas theoretically required for complete combustion yof the fuel, will be within the range oflzl to 2.5:1.

As stated, the process and apparatus of this 'invention are especially adaptedl for the production of unsaturated hydrocarbons, especially acetylene, ethylene and miX` tures of acetylene and'ethylene, by thermallyV cracking light hydrocarbons hereinbefore mentioned. The reaction temperatures for such a process will vary in the approximate range from 1250 F. to3200"V F. In the, acetylene process, the reaction temperature ispreferably f maintained between about 2200 F. and 2600o F., still more preferablyV between about 2400 F. and 26G0"F.`

When mixed acetylene and ethylenestreams are` desired, the preferred' temperature range is between about 17009 F. and 2200" F.; and in the ethylene process, between about l250 F. and 1700 F. `'Ihe reaction timesfor the several processes are in the following approximate ranges: for acetylene, between 0.001 and 0.2 second; for.-

amixture` of acetylene and ethylene, between 0.0.1and 1V 0.2 second;rand for ethylene, between 0.01 and 2 seconds. From this considerationrof reaction temperatures and"1 reaction times, it is Vapparent that the reactiony times vary- V- inverselyvwiththe reaction temperatures, i. e., the higher j the reaction temperature, the shorter the reactionftime;

for a given reaction.

In addition to the light hydrocarbons Vpreviously mentioned,V the process and apparatus of this invention are also well adapted for use 1n processes for the cracking of hydrocarbons which are normally liquid. While it isV gases from the processY of this invention or otherprocesses can be .advantageouslyemployed. When using` a liquid i hydrocarbon, the fuel is introduced into the furnace in'.

vaporized form.

It will be understood by those skilled in thev art-'that the temperature ofthe effluent converted gasesleaving theV cooling or quenching Vcheckerwork will depend; upon jl gauge pressure.

many inter-related factors. Some of these factors include, of course, the particular conversion being effected, the quench temperature level necessary to arrest the particular reaction as desired, the portion and amount of uid passed through the checkerwork for preheat in the preceding exothermic reaction cycle, the physical structure of the furnace, etc. In the production of acetylene according to my process, itis generally preferred that the eluent product gases exit at a temperature below 1800" F., exit temperatures in the range from 600 to l500 F., being more usually employed.

In a now preferred embodiment of my invention, when converting hydrocarbons in an endothermic conversion, pressures in the furnace are held between the range of 20 inches mercury vacuum and 7 pounds per square inch Pressures employed in general in the process of my invention will, of course, depend upon the nature of the reaction being effected and upon the characteristics of available materials of construction.

In the furnace shown in Figure 1, the fuel and the portion of combustion-supporting gas which is not preheated are shown as being introduced into combustion mixture zone as a plurality of mixed streams` through 'lines Vof such size that flame propagation is prevented.

However, it is within the scope of the invention to mix the two gases before introduction into the combustion mixture zone in an external chamber or chambers communicating wtih the combustion mixture zone, in which chamber or chambers all or a portion of the fuel is burned. It is also within the scope of the invention to introduce the fuel and the portion of the combustion-supporting gas separately to the furnace or combustion mixture zone.

In the operation of regenerative furnaces to effect an endothermic conversion, it is often economically desirable to employ a purge after each combustion cycle or after each make cycle, or both. Thus, steam or another inert gas can be passed for a short period through the entire furnace in order to clear the furnace of the gases left therein at the end of the previous cycle. Such expedients are, of course, within the scope of this invention.

Herein and in the claims wherever combustion zone or combustion mixture zone is recited it will be understood by those skilled in the art in possession of this disclosure that the zone may have any desired shape or configuration, or may have one or more than one fluid or fuel inlets thereto. In its operation one or more than one of such inlets can be employed; and even where such inlets are not located equi-distant between the ends of the furnace or of the zone, obviously at different times in different cycles differently located inlets canbe employed.

The present process is applicable to apparatus and methods such as are disclosed in my copending applications Serial No. 462,836, filed October 18, 1954 and its divisional application Serial No. 700,057, filed December 2, 1957, and Serial No. 471,816, filed November 29, 1954, now Patent No. 2,785,212; copending applications of R. R. Goins and I. W. Begley Serial No. 464,112, filed October 22, 1952, now Patent No. 2,792,437, and Serial No. 434,955, filed June 7, 1954; such apparatus and methods being modified according to the teachings of the present invention.

As will be evident to those skilled in the art, various modifications of this invention can be made or followed in the light of the foregoing disclosure and discussion without departing from the spirit or scope of the disclosure or from the scope of the claims.

I claim:

l. In the heating step of the operation of a regenerative furnace having a first heat accumulator zone, another heat accumulator zone, and a reaction mixture zone intermediate said heat accumulator zones, in which step a first uid is passed into and through said first heat accumulator zone, said intermediate reaction mixture zone,

and is withdrawn through said another heat accumulator zone and in which a second fluid is introduced directly intothe said reaction mixture zone, the iiriprovment which comprises introducing another portion of said first fluid into the reaction mixture zone AWithout passingv it through said first heat accumulator zone, and in which process at least a portion of the two said fluids react with each other in an exothermic reaction, the improvement resulting in an increased thermal eiciency iu the opera-l tion of said heating step.

2. A process which comprises passing a first fluid through a first heat accumulator zone, a reaction mixture zone, and finally through another heat accumulator zone, introducing a second fluid and another portion of said first fluid directly into said reaction mixture zone, reacting at least a portion of the two fluids with each other in an exothermic reaction and thereby accumulating heat in said another heat accumulator zone; interrupting the ow of said first and second fluids, passing a material to be endothermically converted through said another heat accumulator zone, said reaction mixture zone and nally through said first heat accumulator zone, said material being heated, converted n an endothermic conversion, and finally cooled during the flow just recited; interrupting the flow of material to be converted, passing another portion of said rst fluid through said anotherV heat accumulator zone, reaction mixture zone, and finally.

through said first heat accumulator zone, introducing another portion of said second uid and a still further portion of said first fluid directly into said reaction mixture zone, reacting at least a part of said two fluids just recited with each other in an exothermic reaction and thereby accumulating heat in said first heat accumulator zone; interrupting flow of said first Vand second iiuids, passingV another portion of said material to be endothermically converted through said first heat accumulator zone, saidrreaction mixture zone, and finally through said another heat accumulator zone, said material being heated, converted in an endothermic conversion,'and nally cooled during the flow just recited.

3. A process which comprises passing a first fluid through a first refractory checkerwork, then through aV combustion-mixture zone, and nally through another refractory checkerwork, introducing a second fluid and another portion of said rst fluid directly into said comv bustion mixture zone, reacting at least a portion of the two fluids with each other in an exothermic reaction and therebyV heating the said another checkerwork to a desired temperature; interrupting the flow of said first and second fluids, passing a material-to be endothermically converted through said another refractory checkerwork, then through said combustion mixture zone and then finally through said first checkerwork, said material being heated, converted in an endothermic conversion, and finally cooled during the flow just recited; interrupting the flow of material to be converted, passing another portion of said first fluid through said another refractory checkerwork, then through said combustion mixture zone, and then finally through said first checkcrwork,

introducing another portion of said second liuid and a f combustion mixture zone, reacting at least a part of Y said two fluids just recited with each other in an exothermic reaction and thereby heating the said first checkerwork to a desired temperature; interrupting flow of said first and second fluids, passing another portion of said material to be endothermically converted through said first checkerwork, then through said combustion mixture zone, and then finally through said another checkerwork, said material being heated, converted in an endothermic conversion, and finally cooled during the ow just recited.

4. The process of claim 3V wherein said first uid is a combustion-supporting gas, said second'uid is a fuel, and said material to be converted in an endothermic reaction comprises an organic compound.;

5. The process of claim 4 wherein said fuel is hydrocarbon, said cor'nbustion-supporting` gas-is selected from the' groupsfconsistin'g ofair-,- oxygen-enrichedair, and oxygen, andsaid' material is a hydrocarbon. Y

6j A process'forproducinga gas'cornprising acetylene which comprises passing -a combustionasupporting gas, selected'f-rom the gijoupconsistingof air, oxygen-enriched airfand` oxygenyt-hrough a first refractoryA checkerworli to preheat said gas, then through a combustion mixture zone, andinally through another refractory checkerwork, introducing afuel and vanother portion ofsaid gas not preheated' into said combustion mixture zone in a predetermined ratio to the'amount` of combustion-supporting gas .being'f passed through said'frst checkerwork, burning at least a part of said fuel with a least a part of the combustion-supporting gas, thereby heating the said another checkerwork toa desired temperature, while maintaininga predetermined ratio of the sum of preheated combustion-supporting gasandthe combustion-supportinggas not preheated to the-said fuel such that said combustion-mixture=zone andsaid another checkerwork will be heated to a temperature sufficient to maintain the temperature of the ensuing endothermic conversion within the range from- 17,00 to 3200 F.; interrupting the flow of said combustion-supporting gas and said fuel, passing hydrocarbonl to beV cracked inV an endothermic conversion throughsaid another refractory checkerwork, then through said combustion mixture zone and then nally throughfsaid firstV checkerwork, said hydrocarbon being heated, at least partially cracked to acetylene, and the product gasescontaining acetylene cooled, during the iiow just recited; interrupting `the ow of said hydrocarbon, passing another. portion of said combustion-supporting gas through-said another refractory checkerwork to preheat said gas, thenrthrough said combustion mixture zone, and `finally through said first refractory checkerwork, introducing another portion of said fuel and a still further portion of said combustion-supporting gas not preheated into saidicombustion mixture zone in said predetermined ratio to they amount of combustion-supporting gasbeing passed through said another checkerwork, burning at least a part of said fuel with at least a part of the combustion-supporting gas, therebyheating said iirstvcheckerwork: to a desired temperature, while maintaining said predetermnedfratio of the sum of preheated combustionsupportingV gas and combustion-supporting gas not preheated to said fuelsuch that said combustion mixture 20neandL said first .checkerwora wil-1 beheuedem atemi perature suuicicntfto maintain. the temperatureuofhthe ensuing' endothermic conversion within therange from 1700 to 3200? F.; interrupting` the .ow ofsaidcombus# tion-supporting gas andsaid fuel, passing yanother portion of said hydrocarbon 4to be crackedin an endothermic conversion through said first refractory-checkerwork, then through saidY combustion mixture zone and then finally -V through said another checkerwork, said hydrocarbon 'be-V ing heated at leastpartially crackdto acetylene, and the product gases containing acetylene' cooled,.during the flow just recited.

7. The processof claim comprises atleast one of the group consisting of methane;

ethane, prcpane, butane and' is'obutane;4 the combustion- Y supporting gas is air; the said predeterminedratioof come bustion-supporting gas not' preheatedto combustion-supporting gas-being preheatedris inthe' rangeof 3:1-to 7:1; and the said predetermined ratio ofthe sum ofcombusa tion-supporting gas preheated and combustion-supporting gas not preheated tol the amount of said gas requiredV theoretically to burn all of saidgfuel is in the range from` 1:1 to 2.5:l.

8. The process of claim 6y wherein the product gases; beingl cooled are quenched to a maximum desiredpre` determined temperature, and the minimum amount of combustion-supporting gas` isv preheated, said minimumv amount being defined asrthe amount-of gas which must be1V preheated'bypassing throughA the refractory checkerworleV 2,692,819 Haschefet'al. Oct. 2'6-,19'5'4- 2,751,424- Hasche June'lg.,l 1956 FOREIGN PATENTS". Y.

583,851 Germany Septr..13,.19335 6 wherein the said'hydrocarbon 

1. IN THE HEATING STEP OF THE OPERATION OF A REGENERATIVE FURNACE HAVING A FIRST HEAT ACCUMULATOR ZONE, ANOTHER HEAT ACCUMMULATOR ZONE, AND A REACTION MIXTURE ZONE INTERMEDIATE SAID HEAT ACCUMULATOR ZONES, IN WHICH STEP A FIRST FLUID IS PASSED INTO AND THROUGH SAID FIRST HEAT ACCUMULATOR ZONE, SAID INTERMEDIATE REACTION MIXTURE ZONE, AND IS WITHDRAWN THROUGH SAID ANOTHER HEAT ACCUMULATOR ZONE AND IN WHICH A SECOND FLUID IS INTRODUCED DIRECTLY INTO THE SAID REACTION MIXTURE ZONE, THE IMPROVEMENT WHICH COMPRISES INTRODUCING ANOTHER PORTION OF SAID FIRST FLUID INTO THE REACTION MIXTURE ZONE WITHOUT PASSING IT THROUGH SAID FIRST HEAT ACCUMULATOR ZONE, AND IN WHICH PROCESS AT LEAST A PORTION OF THE TWO SAID FLUIDS REACT WITH EACH OTHER IN AN EXOTHERMIC REACTION, THE IMPROVEMENT RESULTING IN AN INCREASED THERMAL EFFICIENCY IN THE OPERATION OF SAID HEATING STEP. 